The multiple-species natural biofilms were grown on surfaces of coupons made either of mild steel or
polyethylene. The sizes of the coupons were 20 × 7 × 1 mm. The coupons were submerged into the
tubes containing the API medium followed by culturing at 28 °C under microaerophilic conditions. The
growth was slow, and it took therefore 14 days to produce the mature biofilm with superficial density
of 107 colony-forming units (cfu)/cm2 maximum. The biofilms were grown under aseptic conditions excluding
the contamination with the exterior microflora. Inoculate was a natural microbial community
isolated from soils of petroleum exploration sites (Tatarstan). The community comprised predominantly
aerobic heterotrophs and sulfate-reducing bacteria (SRB). The coupons were subjected to low-temperature
plasma in two ways:
(i) Surfaces of the coupons were treated by plasma jet in ambient air. The samples to be treated were
located at the distance of 7 mm away from the nozzle of the plasma jet.
(ii) Surfaces of the coupons were treated by plasma in a saline solution (9 g of NaCl per 1 L of water).
In this case, the coupons were submerged into a saline solution. This liquid was blown out with
gas bubbles at the rate of 100 cm3/s. Electric discharge was excited inside each bubble. This discharge
generated numerous chemically active plasma agents which were transported due to diffusion
into the liquid and reacted with biofilms.
After plasma treatment of the coupons, biofilms were washed out with a saline solution.
Concentrations of the aerobic heterotrophs and sulfate-reducing bacteria in the rinses were determined.
The number of heterotrophs was determined by culturing cells on the FMH agar. The amount of sulfate-
reducing bacteria was determined by 10-fold titration method using the API medium. The 10-fold
sample was analyzed for the presence of iron sulfide, a metabolite of sulfate-reducing bacteria, which
usually forms a black sediment.